This invention relates in general to semiconductor processing, and more particularly to a process for monitoring the thickness of layers in a semiconductor device.
Metrology of layers of semiconductor material that are formed of the same material of which the immediate underlying layer of semiconductor material is also formed is difficult because both layers display many of the same or similar physical properties. For example, no contrast between n-doped silicon or p-doped silicon and intrinsic silicon can be observed by scanning electron microscopy, which is one of the more common ways to determine layer thickness.
Present calibration methods utilized in such circumstances include destructive techniques such as profilometry, which uses a physical probe to measure a height differential, and transmission electron microscopy, which transmits electrons directly through wafers. Such methods may lead to wafer contamination, physical destruction of wafers, non-uniformity in testing, and/or excessive allocations of cost and time. Thus, optical techniques for determining semiconductor layer thickness are preferable alternatives. However, current optical techniques, such as fourier transform infrared spectroscopy (FTIR) using, for example, a BioRad instrument, or reflectometry using a ThermaWave instrument, for example, measure a thickness change in one semiconductor layer overlying a similar semiconductor layer.
For example, FTIR may seek to measure the thickness of an epitaxial silicon layer formed over a silicon substrate using optical detection of a change in dopant ion concentration. One problem with using FTIR to measure the thickness of particular layers of epitaxial silicon is that smaller thicknesses of silicon epitaxy are likely to be beneath the detection limit of the FTIR technique.
In accordance with the present invention, a process for monitoring the thickness of layers in a microelectronic device is provided that substantially eliminates or reduces disadvantages and problems associated with previous developed systems and methods.
In one embodiment of the present invention, a method is presented for determining the thickness of a thickness of a first layer of material in a semiconductor device using a reflectometer, the first layer of material being disposed outwardly from a second layer of material, the first and second layer of material both including silicon. The method includes generating at least one predicted behavior curve associated with a depth profile of an interface between the first and second layer of material, the predicted behavior curve including at least one expected optical measurement, the depth profile associated with the interface being present at a particular theoretical depth. The method also includes emitting light onto a surface of the semiconductor device. The method further includes collecting at least one optical measurement from portions of the emitted light that are reflected by the semiconductor device. The method additionally includes comparing the at least one optical measurement to the predicted behavior curve and determining the approximate actual depth of the interface in response to the compared optical measurement.
In another embodiment of the present invention, a method is presented for monitoring a thickness of a first layer of material in a semiconductor device using a reflectometer, the first layer of material being disposed outwardly from a second layer of material, the first and second layer of material both comprising silicon.
One advantage of the present invention is that it presents an improved process for monitoring the thickness of semiconductor layers that addresses disadvantages of present monitoring processes. An additional advantage of various embodiments of the present invention is that the thickness of a semiconductor layer of material may be achieved without destroying or contaminating wafers of semiconductor material. A further advantage of various embodiments of the present invention is that a process is presented for monitoring the thickness of material that can be performed on-line with semiconductor device manufacture. Yet another advantage of various embodiments of the present invention is that a process is presented for monitoring the thickness of semiconductor layers and material that allows the thickness of one semiconductor layer to be measured even when such semiconductor layer is formed on a second semiconductor layer having the same or a similar material composition.